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Over the last decade, metamaterials have attracted a great interest
thanks to their potential to expand the range of electromagnetic
properties found in natural materials. In particular, the possibility
of achieving negative refractive index media (NIM) enables us to
implement superlenses and optical storing devices. Since the first
experimental demonstration at microwave frequencies, much effort has
been put in extending negative refraction to the visible spectrum,
where we can take full advantage of NIM properties. For instance, the
superior imaging ability of NIM would be essential for visible
microscopy. The desired features for NIM are low loss and isotropy.
This last property includes polarization independence and
negative-index behavior in all spatial directions. None of these
features have been attained in previous experiments. Thus, the current
challenge is to improve such aspects in order to make NIM suitable for
practical applications.
In this work, we experimentally demonstrate a low-loss multilayer
metamaterial exhibiting a double-negative index in the visible
spectrum, while presenting polarization independence at normal
incidence. This has been achieved by exploiting the properties of a
second-order magnetic resonance of the so-called fishnet structure, in
contrast to previous works that used first-order magnetic resonances,
both related to gap surface plasmon polariton (SPP) modes. The
low-loss nature of the employed magnetic resonance, together with the
effect of the interacting adjacent layers, results in a figure of
merit as high as 3.34. A wide spectral range of negative index is
achieved, covering the wavelength region between 620 and 806 nm with
only two different designs. The fabricated metamaterials are the first
experimental multilayer NIM in the visible spectrum, which entails an
important step towards homogeneous NIM in this range. Finally, we
found that the SPP modes determining the permeability resonance
display weak angular dispersion.

*Financial support by the Spanish Ministerio de Ciencia e Innovacion (contract CSD2008-00066 and FPU grant) is gratefully acknowledged.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.X17.1